Measurement of the separation rate of water from water-in-crude oil emulsions is critical for evaluating performance of a chemical demulsifier used for desalting and dehydration of crude oils in the refining industry. For successful operation of desalting and dehydration processes in a refinery, the best demulsifier chemical must be chosen from a pool of candidate chemicals, often from different supplier companies. Evaluation of demusifiers is further complicated due to relatively low experimental conditions (i.e., below about 195° F. (90° C.)) of most laboratory methods compared to the much higher operating conditions (i.e., about 230° F. (110° C.) to about 300° F. (149° C.)) of most commercial desalters and dehydrators. Therefore, real-world performance of candidate demulsifiers cannot be reliably predicted based on laboratory results at experimental conditions (i.e., below about 195° F.) and must be determined through expensive field trials at commercial operating conditions (i.e., about 230° F. to about 300° F.).
The industry standard for laboratory evaluation of demulsifiers is commonly referred to as a “bottle test.” The bottle test (and its variants) involves monitoring the amounts of water separated from a chemically treated emulsion as a function of time. Such measurements are made in glass bottles/tubes with volumetric markings. The separated water settles at the bottom of the glass bottle/tube and forms an interface with the emulsion on top. The amount of water that has separated is estimated periodically by visual inspection of the interface against the volumetric marks. The demulsifier that causes the fastest water separation at experimental conditions (i.e., below about 195° F.) is assumed to be a good candidate for an expensive field trial at operating conditions (i.e., about 230° F. to about 300° F.), which is much higher than the experimental conditions (i.e., below about 195° F.). The bottle test has at least three disadvantages: 1) it cannot be performed safely at temperatures above about 195° F. due to resulting high pressures, 2) it requires determination of real-world performance of candidate demulsifiers through expensive field trials at commercial operating conditions (i.e., about 230° F. to about 300° F.), and 3) it cannot be automated.
In another laboratory method, a single immersed capacitance/conductance probe is used to measure emulsion stability by measuring the amount of water that has separated from oil indirectly.1 Basically, a water layer is carefully laid down at the bottom of a vessel and an emulsion is carefully spread on top of the bottom water layer. The probe level is set so that conductance is measured in the bottom water layer. As water separates, the separated water becomes part of the bottom water layer. If the salt content of the emulsified water is different than salt content of the initial water, then the electrical properties of the bottom water layer change as the water separates from the emulsion and such change in conductivity is measured by the probe. This method has at least three disadvantages: 1) it is extremely difficult to spread the emulsion on top of the bottom water layer, 2) because it is also limited to lower experimental temperatures, it requires expensive field trials at commercial operating conditions, and 3) it cannot be automated to introduce emulsions.
Another laboratory test that has been developed cannot be used for water-in-crude oil emulsions. Ring electrodes, on the outside of the vessel, are arranged at different depths and used to measure capacitance/conductance of an oil-in-water emulsion.2 Although the principals of this test may initially seem similar to the present invention, as discussed below, there are critical, non-obvious differences. First, for the ring electrodes, a non-conductive vessel is required, which means the vessel must be fabricated of glass, ceramic or polymer. None of these materials can be safely adapted for elevated temperatures (i.e., about 230° F. to about 300° F.) and the resulting elevated pressures. Second, the ring electrodes must be sized for a larger vessel to provide the necessary resolution. Third, the method requires the water phase to be continuous and the measured conductivity to be correlated with the oil volume fraction (and, thus, is similar to methods used to measure water-drop size). Similar to the other laboratory methods, this method has at least two disadvantages: 1) because it is also limited to lower experimental temperatures, it requires expensive field trials at commercial operating conditions, and 2) it cannot be automated to introduce emulsions at temperatures above the boiling point of water (i.e., above about 212° F. (100° C.)).
Other industrially-used methods are not suitable for the laboratory setting. For example, radar is used industrially to measure separation rate by measuring the interface location; however, its high cost and relative large circular cross-sections makes it difficult (if not impossible) to use in a laboratory setting. Microwave (i.e., Agar probes) and gamma radiation (i.e., Tracerco profiler) are other industrially-used methods that may (or may not) work on a laboratory scale, and, further, they are cost prohibitive for a laboratory setting. A mechanical float would not be robust enough for measuring separation rate of water from water-in-crude oil emulsions in the laboratory.
Therefore, there is a need for an accurate laboratory and/or online system and method for measuring separation rate of water from water-in-crude oil emulsions at elevated temperatures.